In the mobile communication system, in order to fight the time-varying characteristic of the wireless fading channel and improve the system throughput, there has appeared the technology which adaptively adjusts the transmission power of the transmitter, modulation and coding scheme and data frame length based on the channel state to obtain the best communication effect, and the technology is known as the adaptive coding and modulation technology, which is the most typical link adaptation technology.
In the Long Term Evolution (LTE) system, the control signaling which needs to be transmitted in the uplink is Acknowledgement/Negative Acknowledgement (ACK/NACK) messages, and three forms which reflect the channel state information (CSI) of the downlink physical channel: a channel quality indication (CQI), a pre-coding matrix indicator (PMI), and a rank indicator. The user equipment (UE) reports the CSI to the base station through the physical uplink control channel (PUCCH) and physical downlink shared channel (PDSCH).
The base station performs scheduling according to the CSI, determines the transmission resource size, frequency location, modulation and coding scheme, the number of the layers for the multiple-input multiple-output spatial multiplexing and the pre-coding matrix for the downlink data, and transmits the downlink data and downlink control information (DCI) on NPRB physical resource blocks (PRB). The downlink control information carries two kinds of information which are IMCS and NPRB. IMCS essentially corresponds to one modulation and coding scheme combination, thereby the terminal can obtain the modulation scheme of the downlink data which is used for demodulation. To obtain the downlink TBS, the terminal looks up the table according to the IMCS to obtain the TBS index ITBS, and then looks up the table according to the ITBS and NPRB to obtain the TBS which is used for decoding the downlink data. In the LTE 36-213 protocol, it defines that, when the number of the spatial multiplexing layers equals to 1, the TBS is given by the element (ITBS, NPRB) in table 1.
TABLE 1TBS under one-layer spatial multiplexingwith the system bandwidth being 10 PRBsNPRBITBS1234567891001632568812015217620822425612456881441762082242563283442327214417620825629632837642434010417620825632839244050456845612020825632840848855263269657214422432842450460068077687263281762563925046007128089361032710422432847258471284096810961224812025639253668080896810961256138491362964566167769361096125614161544101443285046808721032122413841544173611176376584776100011921384160818002024122084406809041128135216081800202422801322448874410001256154418002024228025361425655284011281416173619922280260028561528060090412241544180021522472272831121632863296812881608192822802600298432401733669610641416180021522536285632403624183767761160154419922344279231123624400819408840128817362152260029843496388042642044090413841864234427923240375241364584214881000148019922472298434964008458449682252010641608215226643240375242644776535223552112817362280285634964008458451605736245841192180024082984362442644968554459922561612561864253631123752439251605736620026712148022162984375243925160599267127480
However, for the multi-layer spatial multiplexing, the TBS is obtained from the corresponding table according to NPRB. Taking the two-layer spatial multiplexing as an example, for 1≤NPRB≤55, the TBS is given by the element (ITBS, 2·NPRB) in table 1; for 56≤NPRB≤110, the element (ITBS, NPRB) in table 1 is obtained firstly which is taken as the one-layer TBS (TBS_L1), and then the one-layer to two-layer TBS mapping table (i.e. table 2) under the condition of two-layer spatial multiplexing is looked up to obtain the two-layer TBS (TBS_L2). For the more-layer spatial multiplexing, the LTE protocol 36.213 defines the one-layer to more-layer TBS mapping table, the method for obtaining the TBS is same with that of the two-layer spatial multiplexing, which will not be described repeatedly here.
TABLE 2One-layer to two-layer TBS mapping table under thecondition of two-layer spatial multiplexing.TBS_L1TBS_L21544311216083240167233681736349618003624186437521928388019924008202440082088413621524264221643922280458423444776240847762472496825365160260051602664535227285544279255442856573629845992311262003240645633686712349669683624722437527480388077364008799241368248426485044392876045849144477695284968991251601029653521068055441106457361144859921183262001257664561296067121353669681411272241468874801468877361526479921584082481641685041699287601756891441833695281908099121984810296206161068021384110642215211448229201183223688122162449612576254561296025456135362737614112283361468829296152643057615840317041641632856169923400817568351601833636696190803788819848392322061640576213844236822152438162292045352236884688824496489362545651024264165275227376550562833657336292965925630576616643170463776328566659234008688083516071112366967371237888762083923278704405768117642368847604381687936453529081646888938004893697896510241018405275210552855056110136573361150405925611981661664124464637761284966659213320868808137792711121422487371214685675376149776
After the modulation scheme is given by IMCS, actual rates of the elements in the same ITBS row collectively correspond to, but not strictly equal to one target rate. Table 1 is just designed according to the target rate, however, in table 2, the two-layer TBS and one-layer TBS have the same target rate, the design of the more-layer TBS also follows the corresponding relationship. For one given TBS, its actual rate is related to the number of the resource elements (RE) which can be used to bear the data in one RB in the downlink transmission. At present, in table 1, the numbers of the REs which can be used in one RE are all assumed as 120, except that the number of the REs which can be used in one RE for the last level, i.e., ITBS=26, is assumed as 136. 120 REs are considered for two orthogonal frequency division multiplexing (OFDM) symbols used for control and cell-specific reference signals (CRS) of two antenna ports, and 136 REs are considered for one OFDM symbols used for control and CRSs of four antenna ports. However, for some application scenarios, such as a new carrier type (NCT), the situation that, 156 REs are all used to bear the data, except 12 REs are used for demodulation reference signals (DMRS) in one RB, exists. At this point, if the above way for determining the TBS is directly used, it will cause the actual rate corresponding to the TBS to be decreased, thereby reducing the system frequency spectrum efficiency. In other application scenarios, for example, when one transport block is transmitted on a plurality of sub-frames, the corresponding resources used to bear data will also be increased. In conclusion, since the related TBS determining way is designed based on that the number of the REs which can be used in 1RB is 120 or 136, but in the new application scenarios, the number of the REs which can be used may be different. If the related TBS determining way is directly used, it will cause that the actual rate of the TBS is less than the target rate, and the system frequency spectrum efficiency is reduced. In order to improve the frequency spectrum efficiency and throughput in the new application scenarios effectively, it is necessary to re-consider the TBS design method.